The invention relates to a process for the production of a multi-layered protective and/or decorative coating on a substrate surface, in which
(1) a suitable pigmented base coating composition is applied to the substrate surface,
(2) a polymer film is formed from the composition applied in stage (1),
(3) a transparent aqueous top coating composition containing a water-dilutable polyacrylate resin as the binder and an aminoplast resin as the crosslinking agent is applied to the base layer thus obtained, and
(4) the base layer is then stoved together with the top layer.
The invention also relates to aqueous coating compositions, water-dilutable polyacrylate resins and a process for the preparation of water-dilutable polyacrylate resins.
The process for the preparation of a water-dilutable polyacrylate resin is known. It is used in particular for the preparation of automobile metallic effect lacquerings (compare, for example, U.S. Pat. No. 3,639,147, DE-A-33 33 072 and EP-A-38,127).
For economic and ecological reasons, it is desirable to employ aqueous top coating compositions in stage (3) of the so-called "base coat clear coat" process described above.
It must be possible to apply the top coating compositions by spraying with the aid of automatic lacquering lines. For this, they must have such a high solids content at the spraying viscosity that lacquer films of adequate layer thickness are obtained with one to two spray passes (cross passes), and they must produce stoved lacquer films which exhibit a good appearance (good flow, high gloss, good top lacquer status...).
The aqueous top coating composition disclosed in Example 2 of EP-A-38,127 does not meet all the abovementioned requirements.